Effects of hydrogen peroxide on voltage-dependent K(+) currents in human cardiac fibroblasts through protein kinase pathways

Human cardiac fibroblasts (HCFs) have various voltage-dependent K(+) channels (VDKCs) that can induce apoptosis. Hydrogen peroxide (H(2)O(2)) modulates VDKCs and induces oxidative stress, which is the main contributor to cardiac injury and cardiac remodeling. We investigated whether H(2)O(2) could modulate VDKCs in HCFs and induce cell injury through this process. In whole-cell mode patch-clamp recordings, application of H(2)O(2) stimulated Ca(2+)-activated K(+) (K(Ca)) currents but not delayed rectifier K(+) or transient outward K(+) currents, all of which are VDKCs. H(2)O(2)-stimulated K(Ca) currents were blocked by iberiotoxin (IbTX, a large conductance K(Ca) blocker). The H(2)O(2)-stimulating effect on large-conductance K(Ca) (BK(Ca)) currents was also blocked by KT5823 (a protein kinase G inhibitor) and 1 H-[1, 2, 4] oxadiazolo-[4, 3-a] quinoxalin-1-one (ODQ, a soluble guanylate cyclase inhibitor). In addition, 8-bromo-cyclic guanosine 3', 5'-monophosphate (8-Br-cGMP) stimulated BK(Ca) currents. In contrast, KT5720 and H-89 (protein kinase A inhibitors) did not block the H(2)O(2)-stimulating effect on BK(Ca) currents. Using RT-PCR and western blot analysis, three subtypes of K(Ca) channels were detected in HCFs: BK(Ca) channels, small-conductance K(Ca) (SK(Ca)) channels, and intermediate-conductance K(Ca) (IK(Ca)) channels. In the annexin V/propidium iodide assay, apoptotic changes in HCFs increased in response to H(2)O(2), but IbTX decreased H(2)O(2)-induced apoptosis. These data suggest that among the VDKCs of HCFs, H(2)O(2) only enhances BK(Ca) currents through the protein kinase G pathway but not the protein kinase A pathway, and is involved in cell injury through BK(Ca) channels.